Gage devices for making at least one linear measurement desirably minimize friction and contact between moveable parts. Friction causes wear which can result in error. U.S. Pat. No. 3,422,540 to Worthen describes a device utilizing a leaf spring type reed in a gage head which flexes without friction to adjust to work size.
Another desirable feature of a linear measurement device is to provide rectilinear motion. The above described U.S. Patent utilizes a single flexure point and therefore does not achieve true parallel motion. U.S. Pat. No. 3,193,933 describes a drive which uses parallel flexible arms mounted at one end and connected to a support member at the other end to provide rectilinear motion to the support member. This construction typlifies a device using a rectangular flexure member with four separate flexures at the corners.
Conventional and current construction of parallel mechanical movements for linear measurement devices has concentrated on multipiece assemblies and one piece assemblies that use four separately machined flexures at the corners of a rectangular-shaped flexure member. The use of four separately machined flexure members introduce error since multiple pieces must be joined and errors attendant with the joining of multiple parts is introduced.
True linear motion in a gaging device is highly desirable for the measurement of very small distances. Any accurate or nonparallel motion can result in measurement inaccuracies which must be corrected.
Flexure devices have been used in various force measurement devices. U.S. Pat. No. 4,559,717 to Scire et al disclose a flexure hinge capable of independent xy motion in a single plane free of pitch, roll, yaw, and of motion perpendicular to the plane of motion. U.S. Pat. No. 3,576,128 to Lockery et al discloses a parallelogram-type beam of the type having two transverse holes connected by a slot so as to provide upper and lower beams. Flexible portions are formed adjacent the top and bottom of the holes. The beams are relatively rigid longtitudinal sections extend between the upper halves of each hole and between the lower halves of each hole. This construction results in substantially linear motion. The strains are measured at selected surface portions of the member to obtain a reading indicative of the force being applied. The device described in Lockery et al is force dependent. The greater the force applied, the greater is the force-induced strains. The device is built to resist the force whereby deflection is proportional to the force applied. Heretofore, devices of the type described are not believed to have been used in devices for making linear measurements.